From: Matthias Kaehlcke Subject: Re: [PATCH 3/7] x86, LLVM: suppress clang warnings about unaligned accesses Date: Thu, 13 Apr 2017 16:14:39 -0700 Message-ID: <20170413231439.GG28657@google.com> References: <20170317001520.85223-1-md@google.com> <20170317001520.85223-4-md@google.com> <20170403230158.GA145051@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Cc: Michael Davidson , Michal Marek , Thomas Gleixner , Ingo Molnar , Herbert Xu , "David S. Miller" , Shaohua Li , Alexander Potapenko , Dmitry Vyukov , x86@kernel.org, linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org, linux-raid@vger.kernel.org To: hpa@zytor.com Return-path: Received: from mail-pf0-f173.google.com ([209.85.192.173]:36574 "EHLO mail-pf0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752077AbdDMXOl (ORCPT ); Thu, 13 Apr 2017 19:14:41 -0400 Received: by mail-pf0-f173.google.com with SMTP id o126so34482215pfb.3 for ; Thu, 13 Apr 2017 16:14:41 -0700 (PDT) Content-Disposition: inline In-Reply-To: <20170403230158.GA145051@google.com> Sender: linux-crypto-owner@vger.kernel.org List-ID: El Mon, Apr 03, 2017 at 04:01:58PM -0700 Matthias Kaehlcke ha dit: > El Fri, Mar 17, 2017 at 04:50:19PM -0700 hpa@zytor.com ha dit: > > > On March 16, 2017 5:15:16 PM PDT, Michael Davidson wrote: > > >Suppress clang warnings about potential unaliged accesses > > >to members in packed structs. This gets rid of almost 10,000 > > >warnings about accesses to the ring 0 stack pointer in the TSS. > > > > > >Signed-off-by: Michael Davidson > > >--- > > > arch/x86/Makefile | 5 +++++ > > > 1 file changed, 5 insertions(+) > > > > > >diff --git a/arch/x86/Makefile b/arch/x86/Makefile > > >index 894a8d18bf97..7f21703c475d 100644 > > >--- a/arch/x86/Makefile > > >+++ b/arch/x86/Makefile > > >@@ -128,6 +128,11 @@ endif > > > KBUILD_CFLAGS += $(call cc-option,-maccumulate-outgoing-args) > > > endif > > > > > >+ifeq ($(cc-name),clang) > > >+# Suppress clang warnings about potential unaligned accesses. > > >+KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member) > > >+endif > > >+ > > > ifdef CONFIG_X86_X32 > > > x32_ld_ok := $(call try-run,\ > > > /bin/echo -e '1: .quad 1b' | \ > > > > Why conditional on clang? > > My understanding is that this warning is clang specific, it is not > listed on https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html Actually this warning affects other platforms besides x86 (e.g. arm64), I'll submit a patch that disables the warning on all platforms. Cheers Matthias